Islamic State (IS) fighters have taken full control of the ancient city of Palmyra and have entered the UNESCO World Heritage site containing prized ruins.
The British-based Syrian Observatory for Human Rights said on May 21 that the extremist group now controlled about half of Syria's territory.
It said regime troops pulled back from positions in and around Palmyra, including from an intelligence outpost, a military air base, and a prison following clashes that have killed at least 100 pro-government fighters.
The ruins at Palmyra are one of the world's most renowned historic sites and there were fears the extremists would destroy them as they did major archaeological sites in Iraq.
The city is famous for its 2,000-year-old towering Roman-era colonnades and other ruins and priceless artifacts. Before the war, thousands of tourists a year visited the remote desert outpost.
The fall of the town to the Islamic State group after a week of fighting was an enormous loss to the government, not only because of its cultural significance, but because it opens the way for the extremists to advance to key government-held areas, including Damascus and the Syrian coast to the south.
Next to it are also important gas and oil fields in the country's central region.
With the fall of Palmyra, IS now controls about 40 percent of Syria and almost all of the country's oil fields, which are a major source of revenue for the militant group.
There are fears the IS militants would destroy the ruins as they did major archaeological sites on Iraqi territory.
"I am terrified," said Maamoun Abdulkarim, Syria's director-general of antiquities and museums. "This is a PR battle for Daesh, and they will insist on scoring victory against civilization by destroying" the ancient ruins, he said, using the Arabic acronym for the group.
The fall of Palmyra just days after Islamic State fighters seized the strategic Iraqi city of Ramadi showed the extremists' ability to advance on multiple fronts at opposite ends of a sprawling battlefield that spans the two countries. It also erased any sense that recent IS losses in Tikrit and elsewhere had dealt a major blow to the militants.
The Syrian Observatory for human rights reported that government forces collapsed in the face of IS attacks and withdrew from the town late May 20. Beibares Tellawi, an activist in Homs province, confirmed IS was in control of the town.
He said the militants had reached the notorious Tadmur prison, where thousands of Syrian dissidents have been imprisoned and tortured over the years. The government evacuated what it considered its most important prisoners days ago, but the fate of the rest of the 1,000 or so prisoners was not immediately known.
Syrian state TV acknowledged that pro-government forces had withdrawn from Palmyra, and the IS-affiliated Aaamaq News Agency reported the town was "under the complete control of the Islamic State fighters."
IS fighters had also seized control of the Jazl oil field in the Homs countryside, the Aaamaq report said.
Homs governor Talal Barazzi earlier reported that at least 19 people had died in fighting before the miltants assumed control of the city, including seven civilians and 12 pro-government militiament known as National Defense Forces.
Abdulkarim said workers were able to save hundreds of statues and masterpieces from Palmyra that were transported to safe houses in Damascus.
"But how do you save colonnades that weigh a ton? How do you save temples and cemeteries and, and, and. . .?" he asked.
He appealed to the international community to declare "a red line" around Palmyra and called on the U.S.-led coalition to "at least prevent IS convoys from reaching it."
With reporting by Reuters and dpa